• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.105-106
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• 2003

The spectral eddy viscosity model is investigated through the large eddy simulation of the decaying and forced isotropic turbulence. It is shown that the widely accepted 'plateau and cusp' model overpredicts resolved kinetic energy due to the amplification of energy at intermediate wavenumbers. Whereas, the simple plateau model reproduces a correct energy spectrum. This result overshadows a priori tests based on the filtered DNS or experimental data. An alternative method for the validation of subgrid-scale model is discussed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1806-1813
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• 2003

The stirred tank reactor is one of the most commonly used devices in industry for achieving mixing and reaction. Here we report on results obtained from the large eddy simulations of flow inside the tank performed using a spectral multi-domain technique. The computations were driven by specifying the impeller-induced flow at the blade tip radius. Stereoscopic PIV measurements (Hill et $al.^{(1)}$) along with the theoretical model of the impeller-induced flow (Yoon et $al.^{(2)}$) were used in defining the impeller-induced flow as superposition of circumferential, jet and tip vortex pair components. Large eddy simulation of flow in a stirred tank was carried out for the three different Reynolds numbers of 4000, 16000 and 64000. The effect of different Reynolds numbers is well observed in both instantaneous and time averaged flow fields. The instantaneous and mean vortex structures are identified by plotting an isosurfaces of swirling strength for all Reynolds numbers. The Reynolds number dependency of the nondimeansional eddy viscosity, resolve scale and subgrid scale dissipations is clearly shown in this study.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1290-1298
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• 2003

The stirred tank reactor is one of the most commonly used devices in industry for achieving mixing and reaction. Here we report on results obtained from the large eddy simulations of flow inside the tank performed using a spectral multi-domain technique. The computations were driven by specifying the impeller-induced flow at the blade tip radius. Stereoscopic PlY measurements (Hill et al. $^{(1)}$) along with the theoretical model of the impeller-induced flow (Yoon et al. $^{(2)}$) were used in defining the impeller-induced flow as superposition of circumferential, jet and tip vortex pair components. Large eddy simulation of flow in a stirred tank was carried out for the three different Reynolds numbers of 4000, 16000 and 64000. The effect of different Reynolds numbers is well observed in both instantaneous and time averaged flow fields. The instantaneous and mean vortex structures are identified by plotting an isosurfaces of swirling strength for all Reynolds numbers. The Reynolds number dependency of the non-dimensional eddy viscosity, resolved scale and subgrid scale dissipations is clearly shown in this study.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3367-3382
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• 2023

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian computational fluid dynamics method that has been widely used in the analysis of physical phenomena characterized by large deformation or multi-phase flow analysis, including free surface. Despite the recent implementation of eddy-viscosity models in SPH methodology, sophisticated turbulent analysis using Lagrangian methodology has been limited due to the lack of computational performance and numerical consistency. In this study, we implement the standard and dynamic Smagorinsky model and dynamic Vreman model as sub-particle scale models based on a weakly compressible SPH solver. The large eddy simulation method is numerically identical to the spatial discretization method of smoothed particle dynamics, enabling the intuitive implementation of the turbulence model. Furthermore, there is no additional filtering process required for physical variables since the sub-grid scale filtering is inherently processed in the kernel interpolation. We simulate lid-driven flow under transition and turbulent conditions as a benchmark. The simulation results show that the dynamic Vreman model produces consistent results with experimental and numerical research regarding Reynolds averaged physical quantities and flow structure. Spectral analysis also confirms that it is possible to analyze turbulent eddies with a smaller length scale using the dynamic Vreman model with the same particle size.

• 한국해안해양공학회지
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• 제4권2호
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• pp.91-107
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• 1992

Heaps(1972)가 사용한 천해균질류에 대한 선형 기본방정식을 수심평균류속과 해수면변리를 계산하는 External mode와 수심변이 유속을 계산하는 Internal mode로 분리시킨 다음, Internal mode식에 Galerkin Method를 적용하였다. Internal mode유속을 수평좌표, 시간에 따라 변하는 계수와 대직좌표에 따라 변하는 Basis function들의 곱의 형태로 선형전개하며, 난류확산계수를 포함하는 2차미분항으로부터 해수면에 Homogeneous boundary condition과 해저면에 Sheared boundary condition이 가해지는 Sturm-Liouville system을 구성, Eigenfunctions 해를 구하여 Basis function으로 사용하였다. 모델의 성능을 검토하기 위하여 수립된 모델을 정상균일풍이 가해지는 1차원 수노에 적용하여 Cooper and Pearce(1977)가 제시한 해저면 비활동조건하의 무한 및 유한수노 연직류원분포에 대한 해석각와 비교하였으며, North Sea 규모의 등수심 장방형 Basin(Heaps' Basin)에 적용하여 정상균일풍에 대한 Heaps(1972)의 계산결과와 비교하였다.

• 대한기계학회논문집
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• 제9권6호
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• pp.714-724
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• 1985

본 논문에서는 입자가 부상된 2상유동의 해석에서 여러유동조건의 유동을 공 통적으로 해석할 수 있고 또 유동의 난류구조를 규명할 수 있도록 하기 위해서 2-방정 식 난류모델을 적용하였고 또 지배방정식들 속에 나타나는 1유체와 2유체의 2차 상관 관계들을 모형화 할 때 Taweel and Landau의 스펙트럼 이론을 확장발전시켜 적용하였 다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.103-108
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• 2011

초임계환경에서 작동하는 케로신/액체산소 동축와류형 분사기의 혼합특성을 수치적으로 연구하였다. 케로신 물성치를 계산하기 위하여 써로게이트 모델이 적용되었다. 난류모델은 LES를 기반으로 하였고, 초임계영역의 상태량을 계산하기위해 SRK 상태방정식, 점성계수와 열전도도에 대하여 Chung이 제안한 고압상태 혼합물에 대한 방정식, 확산계수에 대하여 Fuller 이론에 Takahashi가 제안한 고압상태의 특징을 고려한 식을 적용하였다. 연소실 압력변화에 따른 분사기와 연소실에서의 열역학적 물성치와 혼합특성을 관찰하였다. 또한 분사기의 압력섭동 스펙트럼밀도를 분석하였다.